When you handle the RowErrorTextNeeded event and specify error text in the handler, an error glyph appears in the row header unless the DataGridView.ShowRowErrors property is set to false. When the user moves the mouse pointer over the error glyph, the error text appears in a ToolTip.

You can use the RowIndex property to determine the state or value of a row, and use this information to change or modify the ErrorText property. This property is initialized with the value of the row ErrorText property, which the event value overrides.

The following code example demonstrates the use of this type. In the example, an event handler reports on the occurrence of the RowErrorTextNeeded event. This report helps you to learn when the event occurs and can assist you in debugging. To report on multiple events or on events that occur frequently, consider replacing Show with Console.WriteLine or appending the message to a multiline TextBox.

To run the example code, paste it into a project that contains an instance of type DataGridView named DataGridView1. Then ensure that the event handler is associated with the RowErrorTextNeeded event.